Illumination apparatus and vehicular headlamp

Title: Illumination apparatus and vehicular headlamp.Abstract: A headlamp includes (i) a semiconductor laser for emitting laser beams, (ii) a light emitting section that includes a first fluorescent material having a peak of emission spectrum which peak falls within a range from 450 nm to 500 nm, and that emits white fluorescence while being irradiated with exciting light emitted from the semiconductor laser, and (iii) a transmission filter for shielding the laser beams and transmitting the fluorescence emitted from the light emitting section. ...

This Nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2010-244572 filed in Japan on Oct. 29, 2010, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to an illumination apparatus, particularly to a vehicular headlamp, which includes an excitation light source and a light emitting section that emits fluorescence while being irradiated with exciting light emitted from the excitation light source.

BACKGROUND ART

Recently, there has been eagerly studied an illumination apparatus that employs, as illumination light, fluorescence generated by irradiation of a light emitting section, including a fluorescent material, with exciting light emitted from a semiconductor light emitting device such as a light emitting diode (LED) or a semiconductor laser diode (LD) that serves as an excitation light source.

Patent Literature 1 discloses an example of such an illumination apparatus. The illumination apparatus uses a semiconductor laser as an excitation light source so as to obtain a high-luminance light source. The semiconductor laser emits coherent laser beams having a great directivity.

Accordingly, the illumination apparatus can converge and use the laser beams as exciting light without wasting the laser beams at all. Further, the illumination apparatus is designed such that the laser beams do not leak outside the illumination apparatus by, for example, (i) employing, as illumination light, fluorescence emitted from the light emitting section after a light emitting section including a fluorescent material is irradiated with laser beams and/or (ii) providing, on a side where the illumination apparatus emits light, a filter for shielding the laser beams.

SUMMARY

In a field, such as an automotive headlamp, in which white light having a high color temperature is required, an illumination apparatus capable of emitting white light having such a high color temperature has been required.

Coherent components included in laser beams are likely to damage human eyes. In view of the circumstances, a conventional illumination apparatus disclosed in, for example, Patent Literature 1 has been designed such that exciting light emitted from an excitation light source does not leak outside the illumination apparatus. This allows safety of particularly human eyes to be maximally secured. Specifically, in the conventional illumination apparatus, a filter for shielding laser beams emitted from a semiconductor laser is provided in an opening of a reflector. This makes it difficult to increase a color temperature of illumination light by use of the laser beams.

Meanwhile, usage of a blue fluorescent material makes it possible to logically increase the color temperature of illumination light. However, the blue fluorescent material, which has a great light emitting efficiency and is suitable for an illumination apparatus including a semiconductor laser, has been hard to find. As such, it has been difficult to increase the color temperature of illumination light by use of the blue fluorescent material. Patent Literature 1 is silent about a concrete fluorescent material included in a light emitting section. Therefore, of course, the illumination apparatus of Patent Literature 1 is not configured in view of a problem of difficulty in increasing the color temperature of white light emitted from the illumination apparatus.

The present invention was made in view of the problem, and an object of the present invention is to provide an illumination apparatus and a vehicular headlamp each capable of increasing a color temperature of illumination light to be emitted outside corresponding one of the illumination apparatus and the vehicular headlamp.

Solution To Problem

In order to attain the object, an illumination apparatus of the present invention, including: an excitation light source for emitting exciting light; a light emitting section that includes a first fluorescent material having a peak of emission spectrum which peak falls within a range from 450 nm to 500 nm, and that emits white fluorescence while being irradiated with the exciting light emitted from the excitation light source; and a transmission filter for shielding the exciting light and transmitting the fluorescence emitted from the light emitting section.

According to the configuration, the light emitting section emits the fluorescence while being irradiated with the exciting light emitted from the excitation light source, and then the fluorescence is emitted via the transmission filter. In this case, the exciting light does not leak outside the illumination apparatus because the exciting light is shielded by the transmission filter. This makes it possible to prevent human eyes from being damaged by the exciting light emitted outside without being converted into fluorescence (or being scattered).

Further, the light emitting section of the illumination apparatus of the present invention includes the first fluorescent material having the peak of emission spectrum which peak falls within a range from 450 nm to 500 nm, that is, a first fluorescent material containing plenty of blue components. This allows the illumination apparatus of the present invention to increase a color temperature of the white light emitted from the light emitting section, as shown in, for example, FIG. 2. It is therefore possible to emit, as illumination light, white light having a desired color temperature even in a case where the transmission filter for shielding exciting light is provided in the illumination apparatus.

This allows the illumination apparatus of the present invention to emit white light that secures safety and that has a high color temperature.

Note that the transmission filter does not need to shield all exciting light, and to transmit all fluorescence emitted from the light emitting section.

Advantageous Effects of Invention

As described above, an illumination apparatus of the present invention, including: an excitation light source for emitting exciting light; a light emitting section that includes a first fluorescent material having a peak of emission spectrum which peak falls within a range from 450 nm to 500 nm, and that emits white fluorescence while being irradiated with the exciting light emitted from the excitation light source; and a transmission filter for shielding the exciting light and transmitting the fluorescence emitted from the light emitting section.

This allows the illumination apparatus of the present invention to emit white light that secures safety and that has a high color temperature.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1

FIG. 1 is a view schematically showing a configuration of a headlamp in accordance with an embodiment of the present invention.

FIG. 2

FIG. 2 is a graph showing a chromaticity range of white required for a vehicular headlamp, and a view showing a chromaticity of illumination light emitted by a light emitting section in which an oxynitride fluorescent material containing a JEM phase is used as a first fluorescent material.

FIG. 3

FIG. 3 is a graph showing a chromaticity range of white required for a vehicular headlamp, and a view showing a chromaticity of illumination light emitted by a light emitting section in which a Caα-SiAlON:Ce fluorescent material is used as a fluorescent material.

FIG. 4(a)

FIG. 4(a) is a view schematically showing a circuit of a semiconductor laser.

FIG. 4(b)

FIG. 4(b) is a perspective view showing a basic configuration of a semiconductor laser.

FIG. 5

FIG. 5 is a cross-sectional view schematically showing a configuration of a headlamp in accordance with another embodiment of the present invention.

FIG. 6

FIG. 6 is a view showing a positional relationship of an end part of an optical fiber with a light emitting section that are included in a headlamp in accordance with another embodiment of the present invention.

FIG. 7

FIG. 7 is a view schematically showing external appearances of (i) a light emitting unit included in a laser down light in accordance with an embodiment of the present invention and (ii) a conventional LED down light.

FIG. 8

FIG. 8 is a cross-sectional view of a ceiling on which the laser down light is provided.

FIG. 9

FIG. 9 is a cross-sectional view of the laser down light.

FIG. 10

FIG. 10 is a cross-sectional view showing a modified example of a method for providing the laser down light.

FIG. 11

FIG. 11 is a cross-sectional view of a ceiling on which the LED down light is provided.

FIG. 12

FIG. 12 shows a comparison of specifications of the laser down light and the LED down light.

DESCRIPTION OF EMBODIMENTS
Embodiment 1

The following describes an embodiment of the present invention with reference to FIGS. 1 through 6.

Technical Idea of the Present Invention

In a case where (i) a semiconductor laser is used as an excitation light source and (ii) exciting light is emitted outside from the semiconductor laser, the exciting light is likely to damage human eyes because the exciting light mostly contains coherent components. Therefore, an illumination apparatus, including a semiconductor laser as an excitation light source, should be designed so as to shield exciting light. For example, in the illumination apparatus, a transmission filter is provided so as to shield the exciting light. In this case, however, the exciting light and exciting light containing blue components are both shielded by the transmission filter. As such, it has been difficult to increase a color temperature of illumination light (white light) by use of the exciting light. Inventors of the present invention found, in view of the circumstances, that it is possible to increase a color temperature of white light emitted from the light emitting section, by using a fluorescent material containing plenty of blue components as a fluorescent material included in a light emitting section, thereby increasing a color temperature of illumination light emitted from the illumination apparatus.

An illumination apparatus in accordance with an embodiment of the present invention was made on the basis of such a technical idea. According to the illumination apparatus, even in a case where the exciting light is shielded, the color temperature of white light emitted from the light emitting section can be increased by using the fluorescent material containing blue components as the fluorescent material included in the light emitting section. This embodiment exemplifies, as the illumination apparatus in accordance with an embodiment of the preset invention, a headlamp (illumination apparatus or vehicular headlamp) 1 that meets standards of a light distribution property of an automotive headlamp (high beam). Note, however, that the illumination apparatus of the present invention is not limited to this embodiment. The illumination apparatus of the present invention is applicable to (i) a headlamp that meets standards of a light distribution property of an automotive low-beam headlamp (low beam), (ii) a headlamp of vehicles other than automobile or a movable object (such as human, ship, aircraft, submarine or rocket) or (iii) other illumination apparatuses such as a searchlight.

Configuration of Headlamp 1

The following describes a configuration of a headlamp 1 in accordance with the present embodiment with reference to FIG. 1. FIG. 1 is a view schematically showing the configuration of the headlamp 1 in accordance with the present embodiment. As shown in FIG. 1, the headlamp 1 includes a semiconductor laser 2 (excitation light source), an aspheric lens 3, a light guiding section 4, a light emitting section 5, a reflector 6 and a transmission filter 7.

Semiconductor Laser 2

The semiconductor laser 2 functions as an excitation light source for emitting exciting light. The headlamp 1 can include a single semiconductor laser 2, alternatively can include a plurality of semiconductor lasers 2. Further, a semiconductor laser 2 in which each chip has a single light emitting point can be used, alternatively a semiconductor laser 2 in which each chip has a plurality of light emitting points can be used. In the present embodiment, the semiconductor laser 2 in which each chip has a single light emitting point is used.

For example, the semiconductor laser 2 in which each chip has a single light emitting point (one stripe) has an optical output of 1.0-watt, emits laser beams having an oscillation wavelength of 405 nm (bluish purple), and operates at 5 V and 0.7 A. The semiconductor laser 2 is sealed in a package (stem) having a diameter of 5.6 mm. In the present embodiment, 10 (ten) semiconductor lasers 2 are used. That is, the headlamp 1 has a total optical output of 10 W. Note, however, that only one of the 10 semiconductor lasers 2 is shown in FIG. 1 for the sake of convenience.

The oscillation wavelength of the semiconductor laser 2 is not limited to 405 nm. The semiconductor laser 2 can preferably have a peak wavelength (peak wavelength of emission spectrum) which falls within a range from 350 nm to 460 nm, and can more preferably have a peak wavelength (peak wavelength of emission spectrum) which falls within a range from 350 nm to 420 nm.

In a case where the semiconductor laser 2 has an oscillation wavelength which falls within a range from 350 nm to 420 nm, it is possible to broaden the range of choice for a second fluorescent material used in combination with a first fluorescent material (having a peak wavelength of emission spectrum which peak falls within a range from 450 nm to 500 nm) so as to form the light emitting section 5 that emits white light. Specifically, it becomes possible to use, as the second fluorescent material, a fluorescent material having a peak wavelength of emission spectrum, which peak wavelength falls within a range from 580 nm to 650 nm. Further, in a case where the peak wavelength of emission spectrum of the semiconductor laser 2 falls within a range from 350 nm to 420 nm, it is possible to conform such a range to a range of an excitation wavelength of oxynitride fluorescent material containing a JEM phase that is used as the first fluorescent material of the light emitting section 5.

In a case where (i) the oxynitride fluorescent material containing JEM phase is used as the first fluorescent material and (ii) the peak wavelength of emission spectrum of the semiconductor laser 2 has a range from ultraviolet light to bluish purple visible light (not less than 350 nm but not more than 380 nm or less than 400 nm), it is possible to excite, at a high efficiency (approximately 60%), the oxynitride fluorescent material containing JEM phase. Note that the oxynitride fluorescent material containing JEM phase is most efficiently excited in a case where exciting light has a peak wavelength of emission spectrum of 360 nm. Further, the oxynitride fluorescent material containing JEM phase can also be excited at a high efficiency (approximately 50%) even in a case where the peak wavelength of emission spectrum of the semiconductor laser 2 has a bluish purple range from 400 nm to 420 nm.

That is, the oxynitride fluorescent material containing JEM phase can be efficiently excited in a case where the semiconductor laser 2 emits laser beams having a peak of oscillation wavelength which peak falls within a range from 350 nm to 420 nm. It is therefore possible that the light emitting section 5 has a great emission efficiency.

In a case where an oxynitride fluorescent material or a nitride fluorescent material is used as the fluorescent material of the light emitting section 5, it is preferable that (i) the semiconductor laser 2 has an optical output of not less than 1 W but not more than 20 W and (ii) the light emitting section 5 is irradiated with the laser beams having a light concentration which falls with in a range from 0.1 W/mm2 to 50 W/mm2. In this case, it is possible to (a) achieve the light flux and the luminescence that are required for a vehicular headlamp and (b) prevent the light emitting section 5 from being extremely deteriorated by laser beams having a high optical output. That is, it is possible to provide a light source having high light flux and high luminescence while securing a longer operating life.

Note that the laser beams with which the light emitting section 5 is irradiated can have a light concentration of more than 50 W/mm2 in a case where a semiconductor nanoparticle fluorescent material (later described) is used as the fluorescent material of the light emitting section 5.

Aspheric Lens 3

The aspheric lens 3 is a lens through which laser beams emitted from the semiconductor laser 2 enter an incident surface 4a that is an end part of the light guiding section 4. For example, FLKN1 405 manufactured by ALPS ELECTRIC CO., LTD. can be used as the aspheric lens 3. However, a shape and a material of the aspheric lens 3 are not particularly limited, provided that the aspheric lens 3 has the above-described function. But yet, the aspheric lens 3 is preferably made from a heat-resistant material which greatly transmits a light beam having a wavelength of approximately 405 nm which is a wavelength of the exciting light.

The aspheric lens 3 converges laser beams emitted from the semiconductor laser 2 so as to guide the laser beams toward a relatively small incident surface (for example, a surface having a diameter of not more than approximately 1 mm). Therefore, in a case where the incident surface 4a of the light guiding section 4 is large enough for laser beams not to need to be converged, the aspheric lens 3 does not need to be provided.

Light Guiding Section 4

The light guiding section 4 is a light guiding member, having a truncated cone shape, for converging and guiding laser beams emitted from the semiconductor laser 2 toward the light emitting section 5 (a laser beam irradiated surface of the light emitting section 5). The light guiding section 4 is optically coupled to the semiconductor laser 2 via the aspheric lens 3 or directly. The light guiding section 4 includes (i) the incident surface 4a (an incident end part) for receiving the laser beams emitted from the semiconductor laser 2 and (ii) a light emitting surface 4b (light emitting end part) from which the laser beams received by the incident surface 4a is emitted toward the light emitting section 5.

The light emitting surface 4b has an area smaller than that of the incident surface 4a. This causes the laser beams that enter the incident surface 4a to be converged by traveling toward the light emitting surface 4b while being reflected from an inner side surface of the light guiding section 4 and then to be emitted from the light emitting surface 4b.

The light guiding section 4 is made from BK7 (borosilicate crown glass), quartz glass, acrylic resin or other transparent materials. The incident surface 4a and the light emitting surface 4b can be planar or curved.

Further, the light guiding section 4 are not limited to a specific one, and can therefore have a truncated pyramid shape or the light guiding section 4 can be optical fiber, provided that it guides, toward the light emitting section 5, the laser beams emitted from the semiconductor laser 2. Alternatively, the light emitting section 5 can be irradiated, via the aspheric lens 3 or directly, with the laser beams emitted from the semiconductor laser 2 instead of providing the light guiding section 4 in the headlamp 1. Specifically, in a case where the semiconductor laser 2 is not far from the light emitting section 5, the light guiding section 4 does not need to be provided in the headlamp 1.

Composition of Light Emitting Section 5

The light emitting section 5 emits white fluorescence while it is being irradiated with the laser beams emitted from the light emitting surface 4b of the light guiding section 4. In the light emitting section 5, plural types of fluorescent materials, which emit light while being irradiated with laser beams, are dispersed in fluorescent material retention materials (sealing materials). Specifically, the light emitting section 5 includes a first fluorescent material, and a second fluorescent material having a peak of emission spectrum different from that of the first fluorescent material.

The first fluorescent material has, for example, a peak of emission spectrum in a range of wavelength from 450 nm to 500 nm. The second fluorescent material has, for example, a peak of emission spectrum which falls within a range from 580 nm to 650 nm. The upper limit of the range of the second fluorescent material can be greater than 650 nm, provided that the second fluorescent material emits light visible to human eyes. However, the upper limit is preferably 650 nm in view of practicality. The reason is as follows. In a case where the second fluorescent material has a peak of emission spectrum of greater than 650 nm, it becomes impossible to obtain sufficiently bright illumination light because spectral luminous efficacy is too low.

Each of the first and second fluorescent materials is an oxynitride or nitride fluorescent material. A typical example of the oxynitride fluorescent material is a commonly called SiAlON (silicone aluminum oxynitride) fluorescent material. The SiAlON fluorescent material is obtained by (i) replacing some silicon atoms of silicon nitride by aluminum atoms and (ii) replacing some nitrogen atoms of the silicon nitride by oxygen atoms. The SiAlON fluorescent material can be prepared by dissolving alumina (Al2O3), silica (SiO2), a rare earth element and the like in silicon nitride (Si3N4) so as to form a solid solution thereof.

The first fluorescent material is, for example, an oxynitride fluorescent material containing JEM phase (JEM phase fluorescent material). The JEM phase fluorescent material has been confirmed to be produced in a process of adjusting a SiAlON fluorescent material stabilized by a rare earth element. The JEM phase is a ceramics found as a grain boundary phase of a silicon nitride material. The JEM phase is generally expressed by a composition formula M1Al (Si6-zAlz) N10-zOz (note than M1 is at least one element selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu). Namely, the JEM phase is a crystal phase (oxynitride crystal), having a unique atom arrangement, which has a composition in which z is a parameter. The JEM phase is excellent in heat resistance because the JEM phase is a crystal which has strong covalent binding.

It is also preferable that the first fluorescent material be a JEM phase fluorescent material including Ce3+ (JEM phase: Ce fluorescent material). Since the JEM phase fluorescent material contains a Ce component, it is possible to cover, for example, a wavelength domain in which relative luminosity is high in case of scotopic vision because (i) it becomes easy to absorb exciting light having wavelengths which fall within a range of the order of 350 nm to 400 nm thereby obtaining emissions of light from blue to bluish green and (ii) half bandwidth of the emission becomes broad. The JEM phase:Ce fluorescent material has a peak wavelength of 480 nm and an emission efficiency of 60% in a case where an excitation wavelength is 360 nm. The JEM phase:Ce fluorescent material has a peak wavelength of 490 nm and an emission efficiency of 50% in a case where the excitation wavelength is 405 nm. A composition, a manufacturing method and the like of the JEM phase fluorescent material are concretely disclosed in, for example, Patent Literatures 2 through 4.

In other words, the light emitting section 5 includes the first fluorescent material having a peak of emission spectrum which peak falls within a range from 450 nm to 500 nm, and the JEM fluorescent material is used as the first fluorescent material. Note that the first fluorescent material is not limited to the JEM phase fluorescent material. For example, it is therefore possible to use, as the first fluorescent material, an oxynitride or nitride fluorescent material having a peak of emission spectrum which peak falls within a range from 450 nm to 500 nm.

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